The term "standard resistance" or "standard running resistance" is herein used to mean any force which opposes the motion of an automotive vehicle which is driven to keep on rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. The term "running resistance" is herein used to mean any force that opposes the motion of an automotive vehicle, which is driven to keep on rolling over the surface of a road at a constant vehicle speed. Running resistance is equal to standard resistance if an automotive vehicle is driven to keep on rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. Running resistance increases and becomes greater than standard resistance if the automotive vehicle is accelerated to increase speed from the constant vehicle speed. The term "acceleration resistance" is herein used to mean this increment or difference in running resistance that has occurred due to acceleration. Running resistance is greater when the automotive vehicle is driven to keep rolling over the surface of a flat road having gradient greater than 0% at a constant vehicle speed than standard resistance for the same vehicle speed. The term "gradient resistance" is used to mean this increment or difference in running resistance.
JP-A 6-88541 discloses a driving force control system for an automotive vehicle having an engine with an electronically controlled throttle and an automatic transmission. According to this known control system, a target driving torque is determined against current accelerator pedal opening and vehicle speed. First and second throttle opening degrees are calculated. The first throttle opening degree is a function of the target driving torque. The second throttle opening degree is proportional to the accelerator pedal opening degree. The first and second throttle opening degrees are combined to give a combined throttle opening degree. The combined throttle opening degree is applied to an electronically controlled throttle. A proportion of the first and second throttle opening degrees reflected in the lo combined throttle opening degree is determined in response to the accelerator opening degree.
A target engine output torque is determined which accomplishes the corrected target driving force. Over a range of manipulation or opening degree of the vehicle accelerator from zero percent to around fifty percent, the opening degree of the electronically controlled throttle valve is adjusted to accomplish a target driving torque that has been determined as a function of the corrected target driving force. Over a range from around fifty percent to one hundred percent, the opening degree of the throttle is determined as a linear function of the opening degree of the accelerator. This measure is intended to give the vehicle operator acceleration feel fit to the operator's demand.
JP-A 10-266882 discloses an attempt to smooth variation in driving force during operation with small values of accelerator pedal opening degree by referring to a plurality of maps stored against varying values of accelerator pedal opening degree, respectively. Each map contains varying values of target driving force against varying values of vehicle speed. For operation with small values of accelerator pedal opening, a map selected against one value of the accelerator pedal opening and the adjacent map selectable against another value of the accelerator pedal opening that is to be reached upon slightly depressing the accelerator pedal contain two different values of target driving force with a small difference.